Ambient air concentrations of benzene, toluene, ethylbenzene and xylene in bus rapid transit route of Tabriz and health risk assessment

Abstract

Public transportation system plays an important role in the daily transportation of people in mega cities. People waiting at bus stops face to acute and chronic exposure of BTEX compounds emitted from diesel bus exhaust. These compounds may have adverse effects for human health due to the carcinogenic and non-carcinogenic effects and also because of their role in the formation of secondary air pollutants. The aim of this study was to determine and health risk assessment of the ambient concentrations of benzene, toluene, ethyl benzene and xylene in bus rapid transit route of Tabriz. Sampling was done from 7 points (4 bus stations and 3 points between stations) in the summer and winter of 1400. SKC pumps and activated charcoal absorbent tubes were used for sampling. Gas chromatography with flame-ionization detector (GC/FID) was utilized for measuring BTEX compounds. The normality of the data was measured and tested according to Skewness and Kurtosis. To analyze the effect of season, time and location of sampling on the amount of atmospheric pollutants, the analysis of Generalized Estimating Equations (GEE) was used. Data analysis was done using IBM SPSS software version 26 and the level of statistical significance is considered 0.05. Based on the results, BTEX concentrations were significantly higher at BRT stations (170.23±128.20 µg/m3) than at points between stations located along the BRT line (139.74±100.70 µg/m3). Temporal variations showed a significant difference between morning (106.91±91.75 µg/m3) and evening (200.78±120.80 µg/m3) levels, mainly the highest concentrations were observed during rush hours in the evening. Also, on average, the concentration of compounds was higher in winter (190.54±109.74 µg/m3) than in summer (123.69±116.66 µg/m3). The non-cancerous cases of the studied pollutants were lower than the recommended limit of USEPA (HR<1) and is acceptable. The cancer risk for benzene with a value of 1.07×10-7, was less than the threshold value of 1×10-6 and was in the range of negligible risk. While in the points located between the stations with a value of 1.52×10-5, it was more than the threshold value and was in the range of probable risk. The results of present study indicated that the concentrations of BTEX compounds in the ambient air of bus stations exceeded the national and international standards. Therefore, it is essential to take necessary arrangements to control and reduce these pollutants.